Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video decoding. In some embodiments, an apparatus for video decoding includes processing circuitry. The processing circuitry decodes prediction information for a block in a current coded picture that is a part of a coded video sequence. The prediction information is indicative of a merge submode. Then, the processing circuitry constructs, in response to the merge submode, a candidate list of candidate motion vector predictors for the block. The candidate list includes one or more first candidates that are corner neighbors of the block and at least one second candidate that is a side neighbor of the block. Then, the processing circuitry reconstructs the block according to motion information associated with the second candidate.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/595,946, “METHODS FOR MERGE LISTCONSTRUCTION” filed on Dec. 7, 2017, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between theoriginal and reconstructed signal is small enough to make thereconstructed signal useful for the intended application. In the case ofvideo, lossy compression is widely employed. The amount of distortiontolerated depends on the application; for example, users of certainconsumer streaming applications may tolerate higher distortion thanusers of television contribution applications. The compression ratioachievable can reflect that: higher allowable/tolerable distortion canyield higher compression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived fromneighboring area's MVs. That results in the MV found for a given area tobe similar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bedirected from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 ((102) through (106), respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videodecoding. In some embodiments, an apparatus for video decoding includesprocessing circuitry. The processing circuitry decodes predictioninformation for a block in a current coded picture that is a part of acoded video sequence. The prediction information is indicative of amerge submode. Then, the processing circuitry constructs, in response tothe merge submode, a candidate list of candidate motion vectorpredictors for the block. The candidate list includes one or more firstcandidates that are corner neighbors of the block and at least onesecond candidate that is a side neighbor of the block. Then, theprocessing circuitry reconstructs the block according to motioninformation associated with the second candidate.

In an example, the at least one second candidate has a same row numberor a same column number as a corner neighbor of the block. In anotherexample, the at least one second candidate is a top side neighbor or aleft side neighbor of the block.

In an embodiment, a number of the at least one second candidate isassociated with a size of the block.

In some embodiments, the processing circuitry segments the block intoblock segments and inserts the at least one second candidate into thecandidate list based on the block segments.

In an example, the processing circuitry determines whether a size of theblock meets a segment requirement and segments the block into the blocksegments when the size meets the segment requirement.

In an embodiment, the processing circuitry inserts a first indicatorindicative of a first neighboring sub-block into the candidate list. Thefirst neighboring sub-block has a column relationship to a block segmentin the block segments. In another embodiment, the processing circuitryinserts a second indicator indicative of a second neighboring sub-blockinto the candidate list. The second neighboring sub-block has a rowrelationship to the block segment.

To determine whether the size of the block meets the segmentrequirement, in an example, the processing circuitry determines whethera column length of the block is larger than a first length threshold. Inanother example, the processing circuitry determines whether a rowlength of the block is larger than a second length threshold. In anotherexample, the processing circuitry determines whether an aspect ratio ofthe block is out of an aspect ratio range.

To segment the block into the block segments, in an example, theprocessing circuitry divides the block in half to generate intermediateblock segments; and divides the intermediate block segments in half in arecursive manner when the intermediate block segments meet the segmentrequirement.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in accordance with H.265.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is an exemplary schematic illustration of a motion vectorprediction of a block and sub-blocks used for, or affected by, motionvector prediction.

FIG. 9 is an exemplary schematic illustration of vertical motion vectorprediction with uniform and square sub-block dimensions.

FIG. 10 is an exemplary schematic illustration of vertical motion vectorprediction with rectangular and non-uniform sub-block sizes.

FIG. 11 shows a flow chart outlining a process (1100) according to someembodiments of the disclosure.

FIG. 12 shows a flow chart outlining a process (1200) according to someembodiments of the disclosure.

FIG. 13 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. (4. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (415), so as to createsymbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501)(that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621) and anentropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques).

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intra,the general controller (621) controls the switch (626) to select theintra mode result for use by the residue calculator (623), and controlsthe entropy encoder (625) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (621) controls the switch(626) to select the inter prediction result for use by the residuecalculator (623), and controls the entropy encoder (625) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (625) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(772) or the inter decoder (780) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(780); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (772). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (771) (datapath not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503) and (603), and thevideo decoders (310), (410) and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503)and (603), and the video decoders (310), (410) and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503) and (503), and the videodecoders (310), (410) and (710) can be implemented using one or moreprocessors that execute software instructions.

Referring to FIG. 8, according to an aspect of the disclosure, mergemode can be a submode of inter or bi-prediction mode where the residualsignal is not present in the bitstream, and assumed to be zero for allcoefficients including the DC coefficient. When a current block is underdecoding using merge mode, the displacements of pixels in the currentblock may be derived from already decoded spatial/temporal neighboringblocks' motion information.

In an embodiment, a block under merge mode may include an array ofsmaller motion vector units. Each motion vector unit is referred to as asub-block, which can be a K×L number of samples, where K and L arepositive integer numbers. For example, when K and L are four (K=L=4), asub-block includes 4×4 samples, and is referred to as a 4×4 sub-block.Each 4×4 sub-block in the current block may have a different motionvector (or motion vector pair when bi-prediction is used). In anotherexample, when K and L are one (K=L=1), a sub-bock includes 1×1 samples,and is referred to as 1×1 sub-block. Thus, each sample in the currentblock may have a different motion vector (or motion vector pair ifbi-prediction is used).

In some embodiments, when sub-block level motion compensation is used, acandidate list (850) for the merge mode is constructed to includeadditional neighboring sub-block information (e.g., candidate (861),candidate (862) and candidate (863)) that is added based on thesub-blocks in the current block. In an example, when constructing thecandidate list for merge mode, spatial neighboring reference blocks'motion information is to be selected. In addition to the outercandidates on top of the current block at left and right corners (e.g.,A(0, 0) and A(0, N+1) in FIG. 8) as in HEVC, certain additional motioninformation from top candidate positions may be selected into thecandidate list based on the sub-blocks (e.g., spatial characteristics ofsub-blocks) when certain conditions are met. For example, candidate list(850) includes additional candidates A(0, 2) (861) and A(0, N+M) (863).Similarly, in addition to the outer candidates to the left of currentblock at top and bottom corners (e.g., A(0, 0) and L(M+1, 0) as in HEVC,certain additional motion information from left candidate positions areselected into the candidate list based on the sub-blocks (e.g., spatialcharacteristics of the sub-blocks) when certain conditions are met. Forexample, candidate list (850) includes candidate (862). In the followingparagraphs, are a few aspects are disclosed to select such additionalcandidates for merge mode.

FIG. 8 shows a diagram of a current block (810) and surroundingneighboring sub-blocks (820), (830) and (840) that can be used asadditional spatial candidates for the candidate list in the merge mode.In the FIG. 8 example, surrounding neighboring sub-blocks (820), (830),and (840) are 1×1 sub-blocks. The surrounding neighboring sub-block(820) (A(0, 0)) is a top-left sub-block of the current block (810). Thesurrounding neighboring sub-blocks 830 (A(0, 1)-A(0, N+M), N and M arepositive integers) are the above sub-blocks (referred to as topsub-blocks in some examples) of current block (810). As an example, subblock A (0, 2) can be inserted as a candidate in the candidate list, forexample in position (861) The surrounding neighboring sub-blocks (840)(L(1, 0)-L(M+N, 0)) are the left sub-blocks of current block (810).

The order of candidates in the candidate list may have a directinfluence on the coding efficiency of the video coding technology, ascandidates towards the front of the candidate list may be represented byshorter codewords than candidates towards the end. In some embodiments,along the left side (or top side) of the current block (810), more ofthe surrounding neighboring sub-blocks (830) and (840) in the referencearea may be selected as candidates and may be inserted in the candidatelist, for example in positions (861) (862) and (863) only when the size(e.g., the length) left side (or top side) of the current block (810) isof a sufficient, predetermined length. The number of potential candidatepositions in the reference area to be selected on one side of the blockmay be determined by the block size (e.g., length) of this side. As anexample, a comparatively long length side may potentially have moresurrounding neighboring sub-blocks from this side selected as candidatesthan a comparatively short side. Doing so can limit the maximum lengthof the candidate list, which can have advantages from a computationalcomplexity and memory consumption viewpoint.

In one embodiment, a length threshold T is defined such that when theblock length W is greater than T along the current block (810)'s top (orleft) side, the block will be virtually divided into, for example, twosmaller block segments along the top (or left) side, with equal size. Itis noted that, in the context of the disclosed subject matter, the blocksegments are used to determine additional candidates to be inserted inthe candidate list for the merge mode, and may not used as encoding,decoding or prediction units, and thus are referred to as virtual blocksegments in some examples.

In the same or another embodiment, for each divided block segment, ifthe block length is still greater than the given threshold T, then asimilar division operation can continue to divide each block segmentinto even smaller block segments by a predetermined factor, for exampleby halves, until in each block segment the length is no longer greaterthan T. The length threshold can be any integer number. In particular,the length threshold can advantageously be set as a power of 2. In someexamples, a first length threshold is defined for the top side and asecond length threshold is defined for the left side.

In a specific example, when the first length threshold T is defined tobe 32 (e.g., in the units of pixels), and the block length of the topside (width W) of current block (810) is 128 (e.g., in the units ofpixels). The block will be divided into left and right halves of equalsize, each of the block segments will have a top length of 64 (e.g., inthe units of pixels). In this example, 1 level of horizontal splitting,the block with length of 128 on top is divided into 2 (virtual) blocksegments, each with 64 (e.g., in the units of pixels) in length on top.Optionally, each of these two block segments will be further divided byleft and right halves of equal size, having its block length on top as32. In this example, up to 2 levels of horizontal splitting is performedsuch that the block with length of 128 on top is divided into 4 virtualblock segments, each with 32 in length on top.

Further, according to an aspect of the disclosure, the surroundingneighboring sub-blocks (830) and (840) are selectively added in thecandidate list according to spatial relationship with the blocksegments. In some examples, for each divided block segment, a top/leftspatial candidate of its own should be added into the candidate list forthe whole block.

FIG. 9 shows an example that selectively inserts surrounding neighboringsub-blocks in the candidate list (950) based on the spatial relationshipto the block segments, for example into candidate list position (961),(962), (963) and (964). In the FIG. 9 example, assume that the width(block length) W of a current block (910) is twice of the lengththreshold T. In this example, the current block (910) will be dividedinto two horizontal block segments (912) and (915), each with lengthW/2=T. In an example, the surrounding neighboring sub-blocks A(0, 0) andA(0, N+1) are candidates for the whole current block (910) and are addedinto the candidate list (950) (e.g., indicators that are indicative ofthe surrounding neighboring sub-blocks A(0, 0) (951) and A(0, N+1) (952)are added into the candidate list 950). In addition to the candidates ofA(0, 0) and A(0, N+1), other candidates may be added into the candidatelist. In an example, A(0, 1) and A(0, N/2+1) are considered as the topleft and right neighbors of the left half block segment (912), and maybe inserted into the candidate list (e.g., indicators that areindicative of the surrounding neighboring sub-blocks A(0, 1) and A(0,N/2+1) are added into the candidate list 950 for example at positions(962) and (963)). In another example, A(0, N/2) and A(0, N) areconsidered as the top left and right neighbors of the divided right halfblock segment (915), and are inserted into the candidate list (950)(e.g., indicators that are indicative of the surrounding neighboringsub-blocks A(0, N/2) and A(0, N) are added into the candidate list (950)for examples at positions (963) and (964)).

FIG. 10 shows another example that selectively inserts surroundingneighboring sub-blocks in the candidate list (1050) based on the spatialrelationship to the block segments. In the FIG. 10 example, assume thatthe width (block length) W of a current block (1010) is four times ofthe length threshold T. Still assuming a subdivision by a power of 2,the current block (1010) will be divided into four horizontal blocksegments (1011)-(1014), each with length W/4=T. In an example, thesurrounding neighboring sub-blocks A(0, 0) and A(0, N+1) are candidatesfor the whole current block (1010) and are added into the candidate list(1050) (e.g., indicators that are indicative of the surroundingneighboring sub-blocks A(0, 0) and A(0, N+1) are added into thecandidate list (1050) at positions (1051) and (1052)). In addition tothe candidates of A(0, 0) and A(0, N+1), other candidates are added intothe candidate list (1050). In an example, A(0, N/4), A(0, N/2), A(0,3N/4) and A(0, N) are inserted into the candidate list (1050) atpositions (1061), (1062), (1063) and (1064). In another example, A(0,1), A(0, N/4+1), A(0, N/2+1), A(0, 3N/4+1) are inserted into thecandidate list (1050) at positions (1065), (1066), (1067) and (1068).The above is just a discussion of top reference candidates, as anexample, similar methods apply to the block height of the current blockif the block height is taller than a given threshold.

It is noted that in an example, when the length of the top/left side isshorter than T, no additional candidate will be selected.

In some embodiments, the division of a block into block segments can betriggered by an aspect ratio of the block. For example, when the aspectratio is out of an aspect ratio range (e.g., higher than an upperboundary of the aspect ratio range or lower than a lower boundary of theaspect ratio range), the longer side of the block is divided for exampleinto halves. In one embodiment, the aspect ratio range is from ½to 2. Inanother embodiment, the aspect ratio range is ¼to 4.

Aspects of the disclosure also provide candidate ordering techniques forconstructing the candidate list. In some embodiments, the constructionof a candidate list in a merge mode may start from putting the currentblock's top and then left neighboring reference blocks into thecandidate list. According to an aspect of the disclosure, non-squareshape blocks have different priorities of merging into their top or leftneighbors. In some examples, the candidate list is constructed accordingto the shape of current block.

In some embodiments, when the block width is longer than or equal to theblock height, then the candidate list construction may put the currentblock's important (i.e., statistically more likely to be selected,because of the geometry) top neighbors before its left neighbors.Otherwise, when the block width is shorter than the block height, thenthe candidate list construction may put the current block's importantleft neighbors before its top neighbors.

Specifically, in an example, a current block has a rectangle shape ofwidth by height. Using FIG. 8 as example, in one embodiment, whenwidth>=height (e.g., N>M), a candidate entry A(0, N) is put before L(M,0) such as shown in the candidate list (850). Otherwise, whenwidth<height (e.g., N<M), a candidate entry L(M, 0) is put before A(0,N) such as shown in the candidate list (870).

In another embodiment, when width>=height, and when the additional mergecandidates from the top neighbors exist (from virtual block segments asdescribed above), these additional top candidates may be put in front ofthe additional left candidates (if they exist), such as shown in thecandidate list (850). Otherwise, when width<height, and when theadditional merge candidates from the left neighbors exist (from virtualblock segments as described above), these additional left candidates maybe put in front of the additional top candidates (if they exist), suchas shown in the candidate list (870).

In another embodiment, when the block width is longer than or equal tothe block height, then the candidate list construction may put currentthe block's important (frequently selected) left neighbors before itstop neighbors. Otherwise, when the block width is shorter than the blockheight, then the candidate list construction may put the current block'simportant (frequently selected) top neighbors before its left neighbors.

Specifically, in an example, a current block has a rectangle shape ofwidth by height. In one embodiment, when width>=height, a candidateentry L(M, 0) is put before A(0, N), such as shown in the candidate list(870). Otherwise, when width<height, a candidate entry A(0, N) is putbefore L(M, 0), such as shown in the candidate list (850).

In another embodiment, when width>=height, and when the additional mergecandidates from the left neighbors exist (from virtual block segments asdescribed above), these additional left candidates may be put in frontof the additional top candidates (if they exist), such as shown in thecandidate list (870). Otherwise, when width<height, and when theadditional merge candidates from the top neighbors exist (from virtualblock segments as described above), these additional top candidates maybe put in front of the additional left candidates (if they exist), suchas shown in the candidate list (850).

FIG. 11 shows a flow chart outlining a process (1100) according to someembodiments of the disclosure. The process (1100) can be used in thereconstruction of a block coded in inter mode and merge submode, so togenerate a prediction block for the block under reconstruction. Duringthe process (1100), a candidate list may be generated with candidatesthat are added based on certain characteristics of the block, including,for example, size characteristics. In various embodiments, the process(1100) are executed by processing circuitry, such as the processingcircuitry in the terminal devices (210), (220), (230) and (240), theprocessing circuitry that performs functions of the video encoder (303),the processing circuitry that performs functions of the video decoder(310), the processing circuitry that performs functions of the videodecoder (410), the processing circuitry that performs functions of themotion compensation prediction module (453), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the inter encoder (630), theprocessing circuitry that performs functions of the inter decoder (780),and the like. In some embodiments, the process (1100) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1100). The process starts at (S1101) and proceeds to (S1110).

At (S1110), prediction information for a block is decoded. In anexample, the processing circuitry decodes the prediction information,and determines that the prediction information is indicative of a mergesubmode that is a submode of inter or bi-prediction mode.

At (S1120), in response to the merge submode, the processing circuitryconstructs a candidate list that includes first candidates that arecorner neighbors of the block and at least one second candidate that isa side neighbor of the block. In some examples, a corner neighbor is aneighbor to the corners of the block, such as A(0, 0), L(M+1, 0), A(0,N+1), L(M, 0) and A(0, N) in the FIG. 8 example, and a side neighbor isa neighbor to the top side or left side of the block, such as A(0,1)-A(1, N−1), A(0, N+2)-A(0, N+M), L(1, 0)-L(M−1, 0), L(M+2, 0)-L(M+N)in the FIG. 8 example.

At (S1130), the block is reconstructed according to the at least onesecond candidate. In an example, the block is reconstructed based on thecandidate list that includes the at least one second candidate. Then theprocess proceeds to (S1199) and terminates.

FIG. 12 shows a flow chart outlining a process (1200) according to someembodiments of the disclosure. The process (1200) can be used in thereconstruction of a block coded in inter mode and merge submode, so togenerate a prediction block for the block under reconstruction. Duringthe process (1200), a candidate list may be generated with candidatesthat are added based on certain characteristics of the block, including,for example, size characteristics. In various embodiments, the process(1200) are executed by processing circuitry, such as the processingcircuitry in the terminal devices (210), (220), (230) and (240), theprocessing circuitry that performs functions of the video encoder (303),the processing circuitry that performs functions of the video decoder(310), the processing circuitry that performs functions of the videodecoder (410), the processing circuitry that performs functions of themotion compensation prediction module (453), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the inter encoder (630), theprocessing circuitry that performs functions of the inter decoder (780),and the like. In some embodiments, the process (1200) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1200). The process starts at (S1201) and proceeds to (S1210).

At (S1210), prediction information for a block is decoded. For example,the processing circuitry decodes the prediction information, anddetermines that the prediction information is indicative of a mergesubmode that is a submode of inter or bi-prediction mode.

At (S1220), a candidate list is constructed that includes firstcandidates that are corner neighbors of the block. In an example, theprocessing circuitry constructs a candidate list that initially includesfirst candidates that are corner neighbors of the block. In someexamples, a corner neighbor is a neighbor to the corners of the block,such as A(0, 0), L(M+1, 0), A(0, N+1), L(M, 0) and A(0, N) in the FIG. 8example. In the following steps, the processing circuitry will insertone or more second candidates that are the side neighbors based on sizecharacteristics of the block. In some examples, a side neighbor is aneighbor to the top side or left side of the block, such as A(0, 1)-A(1,N−1), A(0, N+2)-A(0, N+M), L(1, 0)-L(M−1, 0), L(M+2, 0)-L(M+N) in theFIG. 8 example.

At (S1230), the processing circuitry determines whether the block meetsa segment requirement. In an example, the processing circuitrydetermines whether a width (e.g., the number of columns of pixels in theblock) or a height (e.g., the number of rows of pixels in the block) islarger than a threshold. When the block meets the segment requirement,the process proceeds to (S1240); otherwise, the process proceeds to(S1290).

At (S1240), the block is divided into block segments that no longer meetthe segment requirement. In an example, the block is repetitivelydivided in half until the segment requirement is no longer met.

At (S1250), additional one or more candidates are inserted into thecandidate list based on the block segments, such as described withreference to FIG. 9 and FIG. 10.

At (S1260), in some embodiments, the candidates in the candidate listcan be ordered according to size characteristics of the block.

At (S1270), the block is reconstructed according to the candidate listthat includes the first candidates and the second candidates. Then theprocess proceeds to (S1299).

At (S1290), the processing circuitry generates the prediction blockaccording to the candidate list without adding the second candidates inthe candidate list. Then the process proceeds to (S1299) and terminates.

It is noted that the process (1200) can be suitably modified. In anexample, the step (S1260) can be skipped.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1349) (such as, for example USB ports of thecomputer system (1300)); others are commonly integrated into the core ofthe computer system (1300) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1300) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units (CPU)(1341), Graphics Processing Units (GPU) (1342), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1343), hardware accelerators for certain tasks (1344), and so forth.These devices, along with Read-only memory (ROM) (1345), Random-accessmemory (1346), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1347), may be connectedthrough a system bus (1348). In some computer systems, the system bus(1348) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1348),or through a peripheral bus (1349). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

MV: Motion Vector

HEVC: High Efficiency Video Coding

SEI: Supplementary Enhancement Information

VUI: Video Usability Information

GOPs: Groups of Pictures

TUs: Transform Units,

PUs: Prediction Units

CTUs: Coding Tree Units

CTBs: Coding Tree Blocks

PBs: Prediction Blocks

HRD: Hypothetical Reference Decoder

SNR: Signal Noise Ratio

CPUs: Central Processing Units

GPUs: Graphics Processing Units

CRT: Cathode Ray Tube

LCD: Liquid-Crystal Display

OLED: Organic Light-Emitting Diode

CD: Compact Disc

DVD: Digital Video Disc

ROM: Read-Only Memory

RAM: Random Access Memory

ASIC: Application-Specific Integrated Circuit

PLD: Programmable Logic Device

LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution

CANBus: Controller Area Network Bus

USB: Universal Serial Bus

PCI: Peripheral Component Interconnect

FPGA: Field Programmable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit

CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information for a block in a currentcoded picture that is a part of a coded video sequence, the predictioninformation being indicative of a merge submode; constructing, inresponse to the merge submode, a candidate list of candidate motionvector predictors for the block, the candidate list including one ormore first candidates from a first set of candidates that includescorner neighbors of the block and, when a size of the block meets asegment requirement, at least one second candidate from a second set ofcandidates that includes a side neighbor of the block, the first set ofcandidates not including the second set of candidates; andreconstructing the block according to motion information associated withone of the at least one second candidate.
 2. The method of claim 1,wherein the at least one second candidate has a same row number or asame column number as a corner neighbor of the block.
 3. The method ofclaim 1, wherein the at least one second candidate is a top sideneighbor or a left side neighbor of the block.
 4. The method of claim 1,wherein a number of the at least one second candidate is associated withthe size of the block.
 5. The method of claim 1, further comprising:segmenting the block into block segments; and inserting the at least onesecond candidate into the candidate list based on the block segments. 6.The method of claim 5, wherein the segmenting the block into the blocksegments further comprises: determining whether the size of the blockmeets the segment requirement; and segmenting the block into the blocksegments when the size meets the segment requirement.
 7. The method ofclaim 5, further comprising at least one of: inserting a first indicatorindicative of a first neighboring sub-block into the candidate list, thefirst neighboring sub-block having a column relationship to a blocksegment in the block segments; and inserting a second indicatorindicative of a second neighboring sub-block into the candidate list,the second neighboring sub-block having a row relationship to the blocksegment.
 8. The method of claim 6, wherein the determining whether thesize meets the segment requirement further comprises at least one of:determining whether a column length of the block is larger than a firstlength threshold; determining whether a row length of the block islarger than a second length threshold; and determining whether an aspectratio of the block is out of an aspect ratio range.
 9. The method ofclaim 6, wherein the segmenting the block when the size meets thesegment requirement further comprises: dividing the block in half togenerate intermediate block segments; and dividing the intermediateblock segments in half in a recursive manner when the intermediate blocksegments meet the segment requirement.
 10. The method of claim 1,further comprising: ordering the one or more first candidates and the atleast one second candidate in the candidate list based on a sizecharacteristic of the block.
 11. An apparatus, comprising: processingcircuitry configured to: decode prediction information for a block in acurrent coded picture that is a part of a coded video sequence, theprediction information being indicative of a merge submode; construct,in response to the merge submode, a candidate list of candidate motionvector predictors for the block, the candidate list including one ormore first candidates from a first set of candidates that includescorner neighbors of the block and, when a size of the block meets asegment requirement, at least one second candidate from a second set ofcandidates that includes a side neighbor of the block, the first set ofcandidates not including the second set of candidates; and reconstructthe block according to motion information associated with one of the atleast one second candidate.
 12. The apparatus of claim 11, wherein theat least one second candidate has a same row number or a same columnnumber as a corner neighbor of the block.
 13. The apparatus of claim 11,wherein the at least one second candidate is a top side neighbor or aleft side neighbor of the block.
 14. The apparatus of claim 11, whereina number of the at least one second candidate is associated with thesize of the block.
 15. The apparatus of claim 11, wherein the processingcircuitry is further configured to: segment the block into blocksegments; and insert the at least one second candidate into thecandidate list based on the block segments.
 16. The apparatus of claim15, wherein the processing circuitry is further configured to: determinewhether the size of the block meets the segment requirement; and segmentthe block into the block segments when the size meets the segmentrequirement.
 17. The apparatus of claim 15, wherein the processingcircuitry is configured to insert a first indicator indicative of afirst neighboring sub-block into the candidate list, the firstneighboring sub-block having a column relationship to a block segment inthe block segments; and/or insert a second indicator indicative of asecond neighboring sub-block into the candidate list, the secondneighboring sub-block having a row relationship to the block segment.18. The apparatus of claim 16, wherein the processing circuitry isconfigured to: determine whether a column length of the block is largerthan a first length threshold; determine whether a row length of theblock is larger than a second length threshold; and/or determine whetheran aspect ratio of the block is out of an aspect ratio range.
 19. Theapparatus of claim 16, wherein the processing circuitry is configured todivide the block in half to generate intermediate block segments; anddivide the intermediate block segments in half in a recursive mannerwhen the intermediate block segments meet the segment requirement.
 20. Anon-transitory computer-readable medium storing instructions which whenexecuted by a computer for video decoding cause the computer to perform:decoding prediction information for a block in a current coded picturethat is a part of a coded video sequence, the prediction informationbeing indicative of a merge submode; constructing, in response to themerge submode, a candidate list of candidate motion vector predictorsfor the block, the candidate list including one or more first candidatesfrom a first set of candidates that includes corner neighbors of theblock and, when a size of the block meets a segment requirement, atleast one second candidate from a second set of candidates that includesa side neighbor of the block, the first set of candidates not includingthe second set of candidates; and reconstructing the block according tomotion information associated with one of the at least one secondcandidate.